Conventionally, ion exchange materials have been represented by polymeric synthetic resins that are generally refered to as ion exchange resins. The ion exchange resins can be classified into particulate or flaky ion exchange resins, ion exchange membranes, ion exchange fibers, and other resins, according to the types of products. There are two types of ion exchange resins, cation exchange resins and anion exchange resins. The ion exchange resins are further classified into strongly acidic cation exchange resins, weakly acidic cation exchange resins, strongly basic anion exchange resins, and weakly basic anion exchange resins according to the degree of acidity or basicity of ion exchange groups.
The strongly acidic cation exchange resin has a sulfonic acid group (R—SO3−H+) as a functional group. As the weakly acidic cation exchange resins, resins having a carboxylic acid group (R—COO−H+), a phosphonic acid group (R—P(O)(O−H+)2), a phosphinic acid group (R—PH(O)(O−H+)), an arsenious acid group (R—OAsO−H+), a phenoxide group (R—C6H4O−H+), or the like as a functional group are known. The strongly basic anion exchange resins have a quaternary ammonium base (R—N+R1R2R3) or a tertiary sulfonium group (R—S+R1R2) as a functional group. The strongly basic anion exchange resin having a quaternary ammonium base of which the groups bonding to nitrogen are only alkyl groups (e.g. methyl groups) is defined as type I. The resin having a quaternary ammonium base of which the groups bonding to nitrogen include an alkanol group (e.g. —C2H4OH) is defined as type II. Type I exhibits basicity a little stronger than that of type II. The weakly basic anion exchange resins have a primary, secondary, or tertiary amine as a functional group. Various types of such resins with different types of amines have been known.
As described above, ion exchange resins are basically classified into four general types depending upon the acidity or basicity of the ionogenic group. As polymer matrices forming these resins, synthetic polymers such as a styrenic polymer, phenolic polymer, acrylic polymer, and methacrylic polymer are used. The matrix structures are classified into a geltype structure, a geltype structure with enlarged mesh sizes (porous structure), and a macroreticular (MR) structure (macroporous structure) according to the difference in the method of synthesis. The gel-type ion exchange resin is obtained by preparing a copolymer of styrene and divinylbenzene (DVB), for example, having a three-dimensional reticular structure by copolymerization in the presence of a catalyst and a dispersant and introducing a functional group into the resulting copolymer. The porous ion exchange resin is obtained by copolymerizing monomers in the presence of an organic solvent that can cause a copolymer to swell to produce a swelled copolymer with a space (gel porosity) larger than that of the gel-type ion exchange resin and introducing a functional group into the resulting copolymer. The MR ion exchange resin is obtained by copolymerizing monomers in the presence of an organic solvent that functions both as a solvent for the monomers and as a precipitant for the copolymer to produce the copolymer as an aggregate of small spherical gel particles, specifically, a matrix having large pores (macropores) among the particles, and introducing a functional group into the resulting copolymer.
In addition to the ion exchange resin particles, organic porous ion exchange resins having continuous pores have been known. For example, porous materials possessing a particle-aggregated structure have been disclosed in F. Svec, Science, 273, 205-211 (1996) and other publications. Japanese Patent Applications Laid-open No. 10-216717, No. 10-192717, No. 10-192716, and No. 8-252579 disclose particle-aggregated porous ion exchange materials in which a mixture of a cation exchange resin and an anion exchange resin is bound using a binder polymer. These particle-aggregated porous ion exchange materials are produced by binding organic fine particles or ion exchange resin particles, into which ion exchange groups have been previously introduced, with a binder polymer, or by filling a specific mold with these fine particles and heating the particles to melt and bind, optionally introducing ion exchange groups into the binder polymer.
Since these particle-aggregated porous materials have a small pore volume and tiny mesopore sizes due to the particle-aggregated structure, their applications to a process at a large flow rate under a low pressure are limited. In addition, ion exchange groups and the like are not uniformly distributed in these particle-aggregated porous materials. Specifically, in these porous structures, ion exchange groups are not present in the binder polymer or, even if present, the structures of the polymer matrix and ion exchange groups in the binder polymer are different from those in the ion exchange resin. In addition, the density of the ion exchange groups in the binder polymer is smaller than that in the ion exchange resin. Such porous structures do not form homogeneous ion exchange materials as a whole. Adsorbed ions thus easily diffuse in the flow direction in a module. In addition, the length of an ion exchange zone in which both the ion adsorbed part and the ion non-adsorbed part are present becomes large, resulting in leakage of a slight amount of the adsorbed ions. Therefore, the module must be replaced frequently.
In an ion adsorption column module commonly used in the art that is filled with a mixture of ion exchange resin particles, feed water is caused to pass through the ion exchange resin layer to remove ionic impurities. To fill the column with the mixture of ion exchange resin particles, it is necessary to provide a supply means to feed and supply a slurry containing the mixture of ion exchange resin particules. In addition, the column must be filled with the slurry so that the slurry is not spilled off from the column. The filling operation is not an easy task. The ion exchange resin particles are regenerated in an upward flow by separating a cation exchange resin and an anion exchange resin by specific gravity and regenerating the resins separately using regenerant chemicals. In an upward flow, only a low regeneration efficiency can be achieved due to ease with which the packed layers are moved and difficulty in separating the ion exchange resins by specific gravity.
Accordingly, an object of the present invention is to provide an ion adsorption module which can be easily filled with an ion exchange material and in which the packed resin layer does not move even if subjected to an upward flow. Another object of the present invention is to provide an ion adsorption module and a water treatment method, wherein the length of the ion exchange zone may be small even at an increased flow rate, allowing the ion exchange apparatus to have a reduced size, and leakage of even a slight amount of adsorbed ions does not occur, resulting in a reduced regeneration frequency and an improved treatment efficiency.